The following methods for manufacturing a non-sintered pellet are known:
(1) Granges method:
A method which comprises supplying a green pellet, together with an iron ore fine, into a first vessel, holding same in the first vessel for a period of about one and a half days to hydrate same, then, supplying said green pellet into a second vessel, holding same in the second vessel for a period of about five days to hydrate same, and then, holding said green pellet in an outdoor yard for about 20 days to allow same to be hydrated, thereby hardening said green pellet to manufacture a non-sintered pellet.
(2) COBO method:
A method which comprises supplying a green pellet into a vessel, and blowing steam under a high pressure at a temperature of about 200.degree. C. into said vessel to hydrate said green pellet in said vessel, thereby hardening said green pellet to manufacture a non-sintered pellet.
(3) Nippon Steel method:
A method which comprises holding a green pellet in an indoor yard for about three days to hydrate same, and then holding said green pellet in an outdoor yard for about five days to hydrate same, thereby hardening said green pellet to manufacture a non-sintered pellet.
However, the methods (1) and (3) above have the problem that these methods require a long period of time for hydrating the green pellet, and the method (2) above involves the safety and economic problem because of requiring high-temperature and high-pressure steam for hydrating the green pellet.
European Patent Provisional Publication No. 0003665 dated Aug. 22, 1979 discloses a method for continuously manufacturing a non-sintered pellet which enables to solve the above-mentioned problems and to hydrate a green pellet in a relatively short period of time without needing high-temperature and high-pressure steam (hereinafter referred to as the "prior art").
More specifically, the prior art discloses a method for continuously manufacturing a non-sintered pellet which comprises continuously supplying a green pellet into a shaft type reactor comprising a pre-treating zone, a hydration reaction zone following said pre-treating zone and a drying zone following said hydration reaction zone, to continuously pass said green pellet sequentially through said pre-treating zone, said hydration reaction zone and said drying zone; blowing a pre-treating gas with a relative humidity of from 80 to 100% and at a temperature of up to 60.degree. C. into said pre-treating zone to pre-treat said green pellet in said zone; blowing a gas for hydration reaction at a temperature of from 90.degree. to 100.degree. C. containing saturated steam into said hydration reaction zone to hydrate said green pellet in said zone; and, blowing a drying gas at a temperature of from 100.degree. to 500.degree. C. into said drying zone to dry said green pellet in said zone, thereby hardening said green pellet in said drying zone to continuously manufacture a non-sintered pellet.
However, the prior art is has the problem that, when hydrating the green pellet in the hydration reaction zone, part of the green pellet disintegrates in the hydration reaction zone. When part of the green pellet disintegrates in the hydration reaction zone, not only is the product yield lowered, but also the resultant disintegration products cause mutual adherence of other sound pieces of green pellet in the shaft type reactor into clusters. Adherence of these clusters onto the inner surface of the side wall of the shaft type reactor causes scaffolding in the shaft type reactor, preventing smooth transfer of the green pellet through the shaft type reactor, and finally makes it impossible to manufacture a non-sintered pellet.
With these problems in view, there is an increasing demand for developing a method and an apparatus for continuously manufacturing a high-strength and high-quality non-sintered pellet at a high yield, which do not cause disintegration of a green pellet in a shaft type reactor when continuously manufacturing a non-sintered pellet by continuously supplying the green pellet into the shaft type reactor comprising a pre-treating zone, a hydration reaction zone following said pre-treating zone and a drying zone following said hydration reaction zone to pass said green pellet sequentially through said pre-treating zone, said hydration reaction zone and said drying zone, and in the meantime hardening said green pellet. However, such a method and an apparatus have not as yet been proposed.